The background description below of the invention does not necessarily describe prior art technology.
A number of different propulsion chain configurations are used with respect to vehicles in general. A gearbox, for example, may be constituted by a manually changed gearbox or an automatically changed gearbox. It is often desirable that heavy vehicles be propelled in a manner that is as comfortable as possible for the driver. This normally means that changes of gear in the gearbox should be carried out automatically, with the aid of control systems of the vehicle. The use of automatic gearboxes in heavy vehicles has, therefore, become more common.
Automatic gear changing for heavy vehicles is often constituted by a change of gear of “manual” gearboxes in which the change operation is controlled by a control system. Such gearboxes thus comprise one pair of cogged wheels for each gear, where the gear ratios are distributed at appropriate intervals. This type of gearbox has the advantage of often demonstrating a higher efficiency than conventional automatic gearboxes. A clutch for such gearboxes may be constituted by a clutch that is controlled automatically by the control systems of the vehicle, in order to couple the engine of the vehicle to the gearbox.
In principle, the clutch in such vehicles needs to be used only during start of the vehicle from stationary, since other gear changing can be carried out by the control systems of the vehicle without the clutch being opened. In cases in which the clutch is constituted by an automatic clutch controlled by the control systems of the vehicle, however, the clutch is often used to open and close the propulsion chain also during change of gear.
Independently of whether the clutch is used during change of gear or not, in order to obtain as comfortable a change of gear as possible, it is required that the driving force in the propulsion chain during the change of gear, and thus also the associated interruption in driving force during change of gear, are controlled such that undesired jerking motion does not occur, while at the same time it is often desirable that the change of gear be carried out with a relatively short interruption in driving force.